What is DRx and DTx in LTE architecture?

By | July 31, 2013

Discontinuous Reception (DRX) and Discontinuous Transmission (DTX) used in LTE architecture for Power Saving.LTE architecture exploits the idea of Discontinuous Reception (DRX) and Discontinuous Transmission (DTX), to provide a concrete solution to the power saving.

Power save protocols in LTE architecture.

  • Discontinuous Reception (DRX)
  • Discontinuous Transmission (DTX)
  • Both reducing transceiver duty cycle while in active operation
  • DRX also applies to the RRC_Idle state with a longer cycle time than active mode
DRx and DTx

DRx and DTx

Long and Short DRX

  • DRX may have long or short “off” durations, configured by the RRC
  • Transition between long DRX and short DRX – Determined by the eNB (MAC commands) or by the UE based on an activity timer
  • A lower duty cycle could be used during a pause in speaking during a voice over IP call
  • When speaking resumes, this results in lower latency
  • For packets arriving at a lower rate, the UE can be off for a longer period of time
  • For packets arriving more often, the DRX interval is reduced during this period

The RRC sets a cycle where the UE is operational for a certain period of time when all the scheduling and paging information is transmitted. The eNodeB knows that the UE is completely turned off and is not able to receive anything. Except when in DRX, the UE radio must be active to monitor PDCCH (to identify DL data). During DRX, the UE radio can be turned off.

The DRX/DTX functionality is an effective way to reduce the UE’s battery power usage, but at the same time introduces further constraints in the scheduler’s tasks. The immediate consequence of them is an average increase of packets delivery delays . The short DRX/DTX represents a further attempt to exploit the inactivity periods of UE to save even more power. This further saving could be remarkable with certain types of tra?c, but can also be very limited with others, like VoIP.

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